1. Field of the Invention
The present invention relates to a membrane body that finds valid employment in the sector of sails for boats and awnings in the field of civil engineering.
2. Description of the Prior Art
In the field of sailing boats, boats are known that are equipped with at least one principal sail, or mainsail, substantially triangular in shape, that is bent vertically on a mast and horizontally to a boom, and a bow, or jib, that is carried slidingly to the bow stay. Needless to say, the sails are of course the means of propulsion of sailing boats, and perform their drive function when they are hoisted, but must be struck when the boat is moored, and must then be gathered in and folded to be placed below deck or stored elsewhere.
It is known that sails are made is such a way as to be able to take on an aerodynamic conformation once they have been hoisted and flattened according to the wind and intended course. The conformation of the sail depends on the ratio between the curves that are assigned both along the front side, which is bent on a stay or along the boltrope of a mast, and along the lower side, which is suitable for remaining free for being bent in a boom, in such a way that the sail, once it has been flattened through the sheets in conditions of use, cuts horizontal curves, each of which is as close as possible to the curvilinear length of a set aerodynamic profile.
As is known, the sails have a negligible thickness in relation to their respective extent and are therefore capable of resistance only to tensile stress. For this, reason, sails are structurally classifiable as membrane bodies, and are therefore preferably reinforceable with tie rods, in such a way as to keep the required lightness and convenience of use. In the sector of sails that is reinforced with tie rods it is known that production proceeds by assembling sailcloths obtained by hot lamination of pairs of panels of plastic material set and reinforced by the intermediate insertion of a plurality of tie rods distributed according to a set pattern, and then by assembling the sailcloths together two by two to form an entire sail as illustrated in U.S. Pat. No. 4,593,639, which is owned by the American company SOBSTAD SAILMAKERS INC., the teachings of which are included for the sake of convenience. Horizon—Performance Sails, a manufacturer of US sails, had already marketed sails using Tape Drive technology in September 1985, which enabled sails to be constructed reinforced with continuous tie rods in carbon or Kevlar applied through an adhesive connection, a technology that was then transferred to the united States sailmaker Ulmer & Kolius.
For the purposes of clarity, it is pointed out that “sailcloth” is taken to mean a cloth or strip of canvas that is connected on respective longitudinal sides through stitching or through gluing to form a sailor a curtain, or an awning.
In U.S. Pat. No. 5,097,7S4 of the us company NORTH SAILS GROUP, INC., the teachings of which are included for the sake of convenience, sails are disclosed consisting of a single panel or cloth having three layers, and particularly an outer base or structural film layer, a structural layer of load bearing yarns, which are disposed over the film layer and an outer protective layer over the yarn layer (column 3, lines 16-19). So sails according to this patent are rigidly reinforced through the intermediate insertion of a plurality of tie rods distributed according to a set pattern.
The sails that are obtained by applying the teachings of the two aforementioned patents individually or jointly have the very particular feature of being particularly stiff in use so as to enable the sails thus constructed to be compared to the wings of aircraft, which are known to be very efficient. In both cases, the sails made of laminate and internally reinforced, produced by implementing the two aforementioned patents have certain drawbacks, including the fact that the adhesive that is distributed on the panels undergoes a process of very rapid ageing, which is followed by progressive loss of flexibility of the sails overall.
The progressive loss of flexibility of the sails thus constructed leads to numerous drawbacks, the effects of which are felt as the sails are hoisted, both for maneuvering and for adjustment and in folding operations that follow the striking. Once the sails are stiffened, they are very difficult to rig, handle and maintain, in addition of course to creating complications both during hoisting and subsequently during striking, above all if such tasks have to be performed quickly at sea in adverse meteorological conditions. In addition, stiffening of the sail slows down the change of tack in bow or stern turns of the principal or mainsail, and involves limitations in the management of the route that it is desired to complete.
Furthermore, once the sails have to be folded, it becomes necessary to pay great attention to limit the number of folds in order not to further impair the state of the already stiffened sail, and to prolong its life as much as possible. It is immediately understandable that this prudence leads not only to loss of time but significant space occupied by the folded sail, with the result that the sail is difficult to manage because it is very bulky, difficult to place in its bag, and to transport.
Naturally, the rapid loss of their mechanical properties makes such sails usable for only a limited time and therefore makes frequent replacement necessary, the costs of which are justified for use in regatta boats used in important competitions, in which the percentage of the investment of the ship owner is consciously high and with it the awareness that the equipment must be replaced frequently to obtain good results.
In the case of leisure boats, in particular in the case of those equipped to be hired, the sails disclosed above are little used because of their respective stiffness inasmuch as on such boats the sails are on return to port preferably wound around the bow stay f as in the case of forward sails, or around the mast or boom in the case of the mainsail. In particular, sails in Dacron are preferred to the sails disclosed above, Dacron is a textile material that is easily windable in a small radius on a rollerjib or is refoldable and very resistant to fatigue-inducing stress, but is elastic. Therefore, by using sails in Dacron, it is implicit that the possibility of having stiff sails once hoisted and made ready to use is foregone. It should be noted that the name Dacron is a registered trademark of the company Du Pont.
In order to produce sails that overcome the drawbacks of the sails made of Dacron, and of the sails of Sobstad and of North Sails according to the teachings of the two patents quoted above, it was decided to use a concept that is currently not applied either to the sector of sails or to the sector of awnings, and in particular a membrane body that shares with sails the same problems of maintenance of the stiffness of the shape used, together with the need to be easily manageable in conditions of folding when at rest.
In the field of awnings made with panels of flexible material reinforced by the tie rods that adhere to the material the foregoing disclosure is confirmed with the sole difference that the panels for the sails are flat when at rest, and assume their shape in combination with the equipment for which they are designed, whilst the flexible membrane bodies that are used to perform the function of awning can be intrinsically convex.